Final Output Filters

From HF Signals
Jump to: navigation, search

We have started to discuss the final output amplifier filtering. The discussion started by noting that we have provision in the schematic for 3 digital outputs for band selection, but can only see one of these (BAND_HI - pin 11 - Arduino D5) being used within the function "setBandswitch". It is this function that currently selects the LPF used based on frequency.

Is was initially proposed that we do something like this:

Filter Ideas.png

Discussion followed and it was suggested that we have only four output filters, primarily so we can keep the current line switching the input LPFs (Processor pin 11, Arduino D5) as already implemented, however, if we were to use logic similar to that below, we could use line D5 for both input and output switching:

Filter Ideas2.png

Initially we will focus on the four filters highlighted in yellow above.


Filter One - 4MHz Cut Off Low Pass

Here is the design from QUCS:

4MLPFDesign.png

Here is the practical information of the components:

4MLPFParts.png

and here is the built filter sweep:

4MHz.png

Filter Two - 11MHz Cut Off Low Pass

Here is the design from QUCS:

11MLPFDesign.png

Here is the practical information of the components:

11MLPFParts.png

and here is the built filter sweep:

11MHz.png

Filter Three - 19MHz Cut Off Low Pass

Here is the design from QUCS:

19MLPFDesign.png

Here is the practical information of the components:

19MLPFParts.png

and here is the built filter sweep:

19M.png


[[Using the CMOS 4028 as the output filter switch ]]

I have today tried some simple experiments with the CMOS 4028 as suggested as a means of switching the output filters. I have connected the following to a Arduino Uno:

4028 LEDs.png

And used the Arduino sketch here as a test file:

[1]

You can see the set up in this photo:

4028 interface.jpg

There should be sufficient comments in the code to explain how to wire the 4028 to the Arduino.

This is my initial idea on how the 4028 can be used to control the filter switching:

4028 Filters.png